Superhard abrasive cutting tools fitted with saw blades, core bits and cutting wheels for use in construction applications are typically classified as either metal matrix bonded (MB) or as metal single layer (SL). The SL cutting tool has a single layer of abrasive grain (or xe2x80x9cgritxe2x80x9d) bonded to a smooth metal substrate by a minimum of bond material so that the abrasive grit is essentially exposed on the cutting surface of the tool. When the cutting surface is presented to the workpiece to be cut, substantially only the abrasive grit contacts the workpiece. Since a substantial portion of the load of the tool is carried by the abrasive grit, the load on each cutting point of the grit is very high. This condition produces high penetration rates and high cutting rates. However, since the SL tool has only a single layer of abrasive, it can no longer effectively cut once that layer is dulled during operation.
The MB tool increases tool life by increasing the number of layers of abrasive grit on the cutting surface. The typical MB tool is made by forming segments of an abrasive-containing metal matrix and attaching those segments to the periphery of a steel substrate. Because abrasive grit is dispersed throughout the segments, the MB cutting tool surface remains effective after the uppermost abrasive grains dull and are removed. Accordingly, MB tools generally have a longer life than SL tools. However, since the abrasive grit is embedded in a metal matrix, both the metal matrix and the abrasive grit are exposed on the tool periphery. When the MB tool is presented to the workpiece, both the abrasive grit and the metal matrix contact the workpiece, thereby lowering the load on each cutting point of the grit (as compared to an SL tool) and producing lower penetration rates and lower cutting rates.
Some metal single layer tools having teeth are known in the art. In one tool, rectangular teeth are provided on the edge of a core drill, and a single metal layer of abrasive grains are bonded to the teeth. During use, the uppermost grains on the teeth cut the workpiece. However, the large size, high concentration and low toughness of the grains are such that these uppermost grains quickly dull when cutting hard surfaces such as masonry, and the penetration rate of the tool quickly falls to zero.
In another tool, angled teeth are provided on the cutting surface of a grinding wheel, and a single metal layer of abrasive grains is electroplated to the teeth. During use, the uppermost grains on the teeth cut the workpiece. However, the weak mechanical nature of the electroplate bond results in the lower levels of grains being peeled from the tooth. Accordingly, the usefulness of the tool is limited to the usefulness of the uppermost layer of grains.
Therefore, it is an object of the present invention to provide a cutting tool having the high penetration rate characteristic of an SL tool and the long life characteristic of an MB tool.
In accordance with the present invention, there is provided an abrasive cutting tool comprising:
a) a substrate surface having a plurality of teeth extending therefrom, each tooth having a surface, and
b) a layer comprising abrasive grains, the layer being chemically bonded to at least a portion of the surface of each tooth to define a plurality of cutting levels parallel to the substrate surface,
wherein the grains have a relative strength index of at least one minute, as measured by the FEPA standard for measuring the relative strength of saw diamonds.
Also in accordance with the present invention, there is provided a method of cutting, comprising the steps of:
a) providing an abrasive cutting tool comprising:
i) a substrate surface having a plurality of teeth extending therefrom, each tooth having a surface, and
ii) a layer comprising abrasive grains, the layer being chemically bonded to at least a portion of the surface of each tooth to define a plurality of cutting levels parallel to the substrate surface, the cutting levels comprising a first uppermost cutting level and a second uppermost cutting level, the grains having a predetermined wear resistance,
b) moving the substrate surface in an intended direction of rotation,
c) contacting the uppermost cutting level of at least one tooth to a workpiece at a point of contact,
d) applying a constant force to the tool directed at the point of contact,
wherein the constant force is sufficient to cut the workpiece, the strength of the bond is sufficient to resist peeling, the predetermined wear resistance of the grains is such that the grains of the first uppermost cutting level fracture under application of the constant force, and the wear resistance of the teeth are such that the portion of the tooth associated with the first uppermost cutting level wears at about the same rate as the grains of the first uppermost cutting level fracture,
thereby causing essentially simultaneous removal of the grains of the first uppermost cutting level from their bond and the portion of the tooth associated with the first uppermost cutting level, and
thereby exposing the grains of the second uppermost cutting level to the workpiece.
Also in accordance with the present invention, there is provided an abrasive cutting tool comprising:
a) a substrate surface having a plurality of teeth extending therefrom, each tooth having a surface and
b) a layer comprising abrasive grains, the layer being chemically bonded to at least a portion of the surface of each tooth to define a plurality of cutting levels parallel to the substrate surface,
wherein the substrate surface has an intended direction of movement, wherein the plurality of teeth includes successive teeth having successively lower uppermost cutting levels in the direction of the intended direction of movement, thereby producing a cutting surface having a negative angle of inclination with respect to the intended direction of movement.
Also in accordance with the present invention, there is provided an abrasive cutting tool comprising:
a) a substrate surface having a plurality of teeth extending therefrom, each tooth having a surface, and
b) a layer comprising abrasive grains, the layer being chemically bonded to at least a portion of the surface of each tooth to define a plurality of cutting levels parallel to the substrate surface,
wherein the substrate surface has an intended direction of movement, wherein at least a portion of each tooth has a face which is inclined at a negative angle with respect to the intended direction of movement, and at least a portion of the grains are bonded to the face having the negative angle of inclination.
Also in accordance with the present invention, there is provided an abrasive cutting tool comprising:
a) a substrate surface having a plurality of teeth extending therefrom, the teeth having a surface and a predetermined wear resistance, and
b) a layer comprising abrasive grains, the layer being chemically bonded to at least a portion of the surface of each tooth to define a plurality of cutting levels parallel to the substrate surface, the grains having a predetermined wear resistance,
wherein the wear resistance of the teeth and the wear resistance of the grains are predetermined such that, when a given cutting level contacts a workpiece under an optimum load, the grains of the given cutting level wear and fracture at about the same rate as the portion of the tooth associated with the given cutting level wears away.